JPH09177578A - Air-fuel ratio control device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep air-fuel ratio constant even in hot restarting. SOLUTION: Cooling water temperature and a physical property temperature differed in rising and falling characteristics from the cooling water temperature are detected by a detecting means 22 and a detecting means 23, respectively, and an intake valve temperature is predicted by a predicting means 24 from the physical property temperature and the cooling water temperature. An equilibrated adhesion amount Mfh and a quantity ratio Kmf are calculated by an arithmetic means 25 on the basis of the intake valve predicted temperature, and by an arithmetic means 26 on the basis of the intake valve temperature, respectively. An adhesion speed Vmf is calculated by an arithmetic means 28 on the basis of the calculated equilibrated adhesion Mfh, the difference from the adhesion Mf at that time (Mfh-Mf), and the calculated quantity ratio Kmf, and the adhesion speed Vmf and the adhesion Mf are added synchronously with fuel injection, whereby the adhesion Mf is renewed by a renewing means 29. A basic injection quantity Tp is corrected with the adhesion speed Vmf, and a fuel injection quantity Ti is calculated by an arithmetic means 30.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control system for an engine, and more particularly to predicting the intake valve temperature when fuel is injected and supplied to the intake valve, and using the intake valve predicted temperature to determine a transient correction amount. Regarding what you want.

[0002]

2. Description of the Related Art Generally, a deviation of an air-fuel ratio from a target value during acceleration / deceleration of an engine adheres to an intake manifold or an intake port, and flows in a liquid state along a wall surface into a cylinder. There are various proposals for performing fuel correction by using the excess and deficiency due to the wall flow fuel as a transient correction amount.

In this case, the equilibrium adhesion amount Mfh and the quantity ratio Kmf and two values are predetermined on the basis of the engine load, the engine speed Ne and the cooling water temperature Tw, and a constant arithmetic expression is used per unit cycle. The adhesion amount (per one injection) (this is called the adhesion speed) Vmf is obtained, and the basic injection amount Tp is corrected by this adhesion speed Vmf. In addition,
The above-mentioned quantity ratio Kmf is a coefficient indicating how much the fuel of the difference (Mfh-Mf) between Mfh and the attached amount (predictive variable) Mf at that time is reflected in the correction of the fuel injection amount.

However, even when fuel is injected not to the intake port but to the intake valve, if the above-mentioned equilibrium adhesion amount Mfh calculated from the cooling water temperature Tw and the distribution ratio Kmf are used, In particular, an air-fuel ratio error occurs immediately after a cold start. Since the wall flow fuel amount at this time depends on the temperature of the intake valve through which the wall flow fuel flows, the temperature difference between the intake valve temperature and the cooling water temperature Tw becomes the estimation error of the wall flow fuel, and the air-fuel ratio error It happens.

Therefore, in the apparatus disclosed in Japanese Patent Application Laid-Open No. 1-305142, the intake valve temperature is predicted, and the predicted intake valve temperature is used in place of the cooling water temperature Tw, whereby Mfh and Kf are calculated.
mf. The intake valve temperature is approximately equal to the cooling water temperature Tw immediately after the startup if a sufficient time has elapsed before the startup, and is a temperature higher than the cooling water temperature Tw by a predetermined value (for example, about 80 ° C.) after the warm-up. Calm down,
Since the change has a first-order delay according to the time constant determined by the intake air amount (see the broken line in FIG. 10A), the balanced intake valve temperature Th and the delay time constant SPTF are set in advance using the load and the rotational speed as parameters. From these, Tf = Th × SPTF + Tf ₋₁ × (1−SPTF) (1) However, Tf ₋₁ : The intake valve predicted temperature using the equation of the previous value of Tf (that is, the equation of the first-order lag). T
f is calculated.

By doing so, it is possible to accurately predict the temperature of the intake valve, which is a representative of the portion where fuel actually adheres, from the start to the completion of warming up.

However, in the actual arithmetic logic, as disclosed in Japanese Patent Laid-Open No. 3-134237, the cooling water temperature Tw starts from a temperature lower by a predetermined value than the cooling water temperature Tw at the time of starting.
A value (this is called a wall flow correction temperature) Twf that converges with a first-order lag toward is given at the time of starting (FIG. 10 (A)).
Dashed line). This is because if the changes in Twf and Tf are the same, they can be handled in exactly the same way on the arithmetic logic.

The formula for calculating Twf (initial value Inwft) is as follows: Twf = Twf _{−1 sec} + (Tw−Twf) × Fltsp (2) where Tw: Cooling water temperature Twf ₋₁ sec: Twf before 1 sec. Fltsp: A temperature change rate during filing.

[0009]

By the way, in the conventional intake valve temperature predicting method, since it is premised that the actual intake valve temperature and the cooling water temperature Tw are equal at the time of starting, the engine temperature is the same as that at the time of hot restart. If the cooling water temperature and intake valve temperature are not equal at restart due to the stop conditions of the engine (for example, engine temperature immediately before stop, elapsed time from stop to restart, temperature at that time, etc.), the intake valve at restart The temperature cannot be predicted accurately, so Mfh and Kmf
There is an error in the calculation of, and as a result the air-fuel ratio cannot be kept constant (exhaust emission and fuel consumption deteriorate).

For example, as shown in FIG. 10 (B), when the engine is stopped while the temperature of the cooling water after warming up is 80 ° C., both the cooling water temperature and the intake valve temperature decrease,
After a sufficient amount of time, both will settle at 20 ° C, and at the subsequent restart (cold start), 20 ° C
When Tf is calculated by using as an initial value, Tf agrees well with the actual intake valve temperature. On the other hand, when restarting (hot restart) is performed in a state in which the time has not elapsed after the engine is stopped, for example, when the cooling water temperature is 30 ° C. (the intake valve temperature is higher than this), 30 ° C.
Since Tf is calculated using as an initial value, Tf is often estimated to be higher than the actual intake valve temperature. According to Tf estimated to be higher than this, the transient correction amount Kathos is insufficient and the air-fuel ratio becomes lean. Of.

Therefore, according to the present invention, the air-fuel ratio is detected even at the time of hot restart by detecting the physical property temperature having different rising and falling characteristics from the cooling water temperature and predicting the intake valve temperature from the detected physical property temperature and the cooling water temperature. The purpose is to keep constant.

[0012]

According to the first invention, FIG.
As shown in, means 21 for calculating the basic injection amount Tp according to the operating conditions, means 22 for detecting the cooling water temperature, and means 23 for detecting the physical property temperature having different rising and falling characteristics from the cooling water temperature, A means 24 for predicting the intake valve temperature from the physical property temperature and the cooling water temperature, and an equilibrium adhesion amount M based on the intake valve predicted temperature, engine load and engine speed.
means 25 for calculating fh, means 26 for calculating the quantity ratio Kmf based on the intake valve temperature, engine load and engine speed, and the calculated equilibrium adhesion amount Mfh
And a means 27 for calculating a difference (Mfh-Mf) from the amount Mf of adhesion at that time, and an adhesion speed V based on the amount of adhesion of the difference (Mfh-Mf) and the calculated amount ratio Kmf.
means 28 for calculating mf, means 29 for updating the adhesion amount Mf by adding the adhesion speed Vmf and the adhesion amount Mf in synchronization with fuel injection, and the adhesion speed Vmf
The means 30 for calculating the fuel injection amount Ti by correcting the basic injection amount Tp and the means 31 for supplying the injection amount of fuel to the intake pipe are provided.

In a second aspect based on the first aspect, the physical property temperature is a catalyst temperature, and the intake valve temperature is predicted by interpolation from the catalyst temperature and the cooling water temperature.

In a third aspect based on the second aspect, the interpolation coefficient is set to a value corresponding to the difference between the catalyst temperature and the cooling water temperature.

In a fourth aspect based on the first aspect, the physical property temperature is an oil temperature, and the intake valve temperature is estimated by extrapolation from the oil temperature and the cooling water temperature.

In a fifth aspect based on the fourth aspect, the extrapolation coefficient is set to a value corresponding to the difference between the oil temperature and the cooling water temperature.

[0017]

[Function] It is difficult to predict the intake valve temperature at the time of hot restart only by the cooling water temperature, but the cooling water temperature rises,
When a physical property temperature with different falling characteristics is detected, it is possible to accurately predict the intake valve temperature from the start from the correlation between the detected physical property temperature, cooling water temperature, and intake valve temperature, so even during hot restart the air-fuel ratio Is kept constant.

[0018]

In FIG. 1, intake air passes from an air cleaner through an intake pipe 8, and fuel is injected from a fuel injection valve 7 to an intake valve of an engine 1 based on an injection signal from a control unit (abbreviated as C / U in the drawing) 2. Is jetted toward. The gas burned in the cylinder is introduced into the catalytic converter 10 through the exhaust pipe 9, where the harmful components (C
O, HC, NOx) are cleaned by a three-way catalyst and discharged.

The flow rate Qa of intake air is detected by a hot wire type air flow meter 6, and the flow rate is controlled by an intake throttle valve 5 which works in conjunction with an accelerator pedal.

The air amount signal from the air flow meter 6 is an air-fuel ratio sensor 3 for detecting the oxygen concentration in the exhaust gas, a crank angle sensor 4 for outputting a crank angle reference position signal (Ref signal) and an angle signal, and a water jacket. It is input to the control unit 2 together with the signals from the water temperature sensor 11 that detects the cooling water temperature Tw and the starter switch 12 that detects the operation of the starter.

In the control unit 2, the basic injection pulse width Tp is calculated from the intake air amount detected by the air flow meter 6 and the engine speed Ne, and the transient correction amount Kathos is added to this Tp during acceleration / deceleration. Fuel is being corrected. Since the transient correction amount Kathos is specifically a correction amount for the fuel wall flow, it works not only at the time of acceleration / deceleration but also at the time of startup when the fuel wall flow changes greatly.

In this case, since the wall flow fuel amount largely depends on the temperature of the portion where the wall flow fuel flows, when all the fuel is injected from the injection valve toward the back of the intake valve, the intake valve It is necessary to predict the temperature and use this intake valve predicted temperature to calculate the transient correction amount Kathos.

However, since the conventional intake valve temperature predicting method is premised on that the actual intake valve temperature and the cooling water temperature Tw are equal at the time of starting, it depends on the engine stop condition, such as at the time of hot restart, at the time of starting. When the intake valve temperature and the cooling water temperature are not equal to each other, the intake valve temperature at the time of restart cannot be accurately predicted, an error occurs in the calculation of Mfh and Kmf, and as a result, the air-fuel ratio can be kept constant. Not possible (exhaust emission and deterioration of fuel efficiency will occur).

To deal with this, in the present invention, a physical property temperature (for example, a catalyst temperature or an oil temperature) whose rising and falling characteristics differ from the cooling water temperature depending on the heat transfer amount and the operating state of the engine.
Is detected, and the intake valve temperature is predicted from the detected physical property temperature and cooling water temperature.

For example, when the engine is started from the state where the cooling water temperature is 20 ° C. (however, the engine is started after the cooling water temperature = the actual intake valve temperature after a sufficient time has passed since the last engine stop) And when the engine is stopped at 80 ° C. after warming up, the cooling water temperature Tw and the catalyst temperature T
c and intake valve temperature changes are shown in FIGS. 2A and 2B, respectively, the intake valve temperature is between Tc and Tw.
The intake valve temperature can be obtained by the interpolation of Tw and Tw.
The arithmetic expression in this case is Tf = Tw + (Tc−Tw) × TTC (3) where Tf: intake valve predicted temperature Tw: cooling water temperature Tc: catalyst temperature TTC: interpolation coefficient. It is difficult to predict the intake valve temperature only by Tw, but by detecting the physical property temperature (that is, the catalyst temperature) having different rising and falling characteristics depending on the amount of heat transfer and the operating state of the engine, the physical property temperature, Tw and By utilizing the correlation with the intake valve temperature, it is possible to accurately predict the intake valve temperature.

When the oil temperature is used instead of the catalyst temperature,
As shown in FIGS. 3A and 3B, the intake valve temperature is the oil temperature To,
Since it comes outside the cooling water temperature Tw, the intake valve temperature can be predicted by extrapolation of To and Tw. The arithmetic expression in this case is Tf = Tw + (Tc−Tw) × TTO (4) where Tf: intake valve predicted temperature Tw: cooling water temperature To: oil temperature TTO: extrapolation coefficient.

As described above, according to the present invention, the intake valve temperature is accurately predicted from the catalyst temperature (or oil temperature) and the cooling water temperature by utilizing the correlation between the hand catalyst temperature, the cooling water temperature and the intake valve temperature. , It is possible to accurately calculate Mfh and Kmf from the start, and as shown by the solid line in FIG. 4, the air-fuel ratio can be kept constant even during hot restart.

Further, since the sensor for detecting the catalyst temperature is usually attached, it is not necessary to provide it again.

Next, the case of predicting the intake valve temperature from the catalyst temperature and the cooling water temperature will be described with reference to the following flow chart.

First, the flow chart of FIG. 5 is for calculating the wall flow correction temperature Twf, for example, 1 sec.
It is executed every time (or every 10 ms).

In step 1, it is checked whether or not firing is in progress. If firing is in progress, the process proceeds to step 2 and subsequent steps. In step 2, the cooling water temperature Tw and the catalyst temperature Tc
And the difference Tc−Tw between them in step 3
To the table having the contents shown in FIG.
C is obtained, and the predicted intake valve temperature Tf is obtained by the above equation (3) in step 4 using the interpolation coefficient TTC, the cooling water temperature Tw, and the catalyst temperature Tc. Then, in step 5, Twf = Tf-80 ° C. The wall flow correction temperature Twf is calculated by the equation (5).

Since the interpolation coefficient TTC differs depending on the difference between the catalyst temperature Tc and the cooling water temperature Tw, Tc-Tw as shown in FIG.
The value depends on. Further, the extrapolation coefficient TTO of the above equation (4) is also given according to To-Tw.

The flowchart of FIG. 7 shows the transient correction amount Kat.
It is for calculating hos, this routine is 10m
Execute in s cycles.

First, in step 11, the equilibrium adhesion amount Mfh
Is calculated using the three parameters Ne, Tp, and Twf.

Here, the data of Mfh is the cooling water temperature T
Since it is given in advance for w, T instead of Tw
Determined using wf. In the case of the cooling water temperature, for example, the actual water temperature Tw is the reference temperature Tw0 to Tw4 (T
w0 >>...> Tw4), it is determined which of the temperature regions is divided, and if Tw ≧ Tw1 is assumed, then
Reference temperature T that is the temperature closest to Tw and higher than Tw
w0 and the reference temperature Tw, which is also lower than Tw
From the map for 1 to map values Mfh0 and Mfh1 (M for Tw0 and Tw1) corresponding to Ne and Tp at that time.
fh) is obtained, Mfh = Mfh0 + (Mfh1−Mfh0) × (Tw0−Tw) / (Tw0−Tw1) (6) ) Is calculated (linear interpolation calculation formula), Mfh is calculated. The equilibrium adhesion amounts Mfh0 to Mfh4 with respect to the reference temperatures Tw0 to Tw4 are obtained by actual measurement using Ne and Tp as parameters.

The method of obtaining Mfh is not limited to this, and as disclosed in Japanese Patent Laid-Open No. 3-134237, Mfh = Tp × Mfhtvo (7) where Mfhtvo: adhesion ratio But it doesn't matter.

A coefficient representing the rate at which the adhesion amount (prediction variable) Mf at the present time approaches Mfh thus obtained per unit cycle (for example, every one rotation of the crankshaft). (That is, the quantity ratio) kmf is calculated in step 12 from the product of the basic quantity ratio Kmfat and the quantity ratio rotation correction factor Kmfn.

Here, Kmfat is a value obtained by referring to the map from Tp and Tw, and is set to increase as Tp increases, for example. Here, Twf is used instead of Tw. Also, K
mfn is a value obtained from Ne by referring to a table, and is set to increase as the rotation speed Ne decreases, for example.

The amount ratio Kmf thus obtained is calculated in step 13 by multiplying the difference between Mfh and the present amount Mf of adhesion, that is, Vmf = (Mfh-Mf) × Kmf (8) Velocity (adhesion amount per unit cycle)
Calculate Vmf.

Mf is a predictive variable of the amount of adhesion at that time, therefore the amount of adhesion of (Mfh-Mf) indicates the excess or deficiency amount from the equilibrium amount of adhesion, and this value (Mfh-Mf) becomes the volume ratio Kmf. Will be further corrected.

After the deposition speed Vmf is obtained in this way, in steps 14 and 15, Vmf is further corrected by the correction rate Ghf for preventing over lean at the time of deceleration when using light fuel, to the basic injection pulse width Tp. The transient correction amount Kathos is obtained, and the flow of FIG. 7 ends.

The flowchart of FIG. 8 shows a process for calculating the final fuel injection pulse width Ti in consideration of the transient correction amount Kathos thus obtained, which is also 10
It is executed in ms cycle.

In step 21, the intake air amount Q at that time
a and a basic injection pulse width Tp (= K · Qa / N) at which a predetermined air-fuel ratio (for example, a stoichiometric air-fuel ratio) is obtained from the rotational speed Ne.
e, where K is a constant), and in step 22, a feedback correction coefficient α determined based on the output of the air-fuel ratio sensor 3 to a value obtained by adding the transient correction amount Kathos to this value.
And the other correction coefficient COEF are multiplied, and the invalid pulse width Ts is further added to obtain the final fuel injection pulse width Ti.

The flow chart of FIG. 9 is a flow chart synchronized with the injection timing (specifically, Ref signal synchronization), and when the predetermined injection timing is reached, Ti is transferred to the output register in step 31 to perform the injection.

In step 32, the deposition rate Mm used in the next process is calculated using the deposition rate Vmf obtained by the above equation (6).
f is _{calculated in advance} by the equation Mf = (Mf _-1Ref ) + Vmf (9).

Mf _-1Ref in the equation (9) means the amount of adhesion at the end of the previous injection (before unit rotation), and the value obtained by adding Vmf added at the time of this injection to this is the time when the current injection ends. Is the adhesion amount Mf. The value of the adhesion amount Mf is used in the next calculation of Vmf. Mf in the equation (8) is the value immediately before the calculation of Vmf, whereas Mf on the left side of the equation (9) is the value immediately after the calculation of Vmf. Therefore, in terms of content, the value of Mf in Eq. (8) is changed to Mf _{-1Ref on the} right side of Eq. (9).
Then, Mf on the left side of the equation (9) is calculated.
The fact that Mf and Mf _-1Ref appear in equation (9) is because the amount of adhesion is _cyclically updated for each unit rotation, so it is necessary to distinguish the previous value from the current value. Because there is.

Regarding the engine load as a parameter for obtaining the above Mfh and Kmf, the basic injection pulse width T in the L-Getronic system MPI shown in FIG.
However, the intake pipe negative pressure is used in the D-Jetronic system MPI, and the α-N flow rate QH0 is used in the so-called α-N system and MPI. It can be used as a load.

Finally, in the embodiment, the transient correction amount Kath is calculated by using the wall flow correction temperature Twf as the intake valve predicted temperature.
As described in the case of calculating os, the estimated intake valve temperature Tf
It goes without saying that Kathos can also be calculated using itself.

[0049]

EFFECTS OF THE INVENTION It is difficult to predict the intake valve temperature at the time of hot restart only by the cooling water temperature, but in the first invention, the physical property temperature whose rising and falling characteristics are different from the cooling water temperature is detected, and Since the intake valve temperature is predicted from the detected physical property temperature and the cooling water temperature, the intake valve temperature can be accurately predicted from the restart, and the air-fuel ratio can be kept constant even during hot restart.

[Brief description of the drawings]

FIG. 1 is a control system diagram of a first embodiment.

FIG. 2 is a waveform diagram showing changes in cooling water temperature Tw, catalyst temperature Tc, and intake valve temperature when the engine is started from a state where the cooling water temperature is 20 ° C. and when the engine is stopped at 80 ° C. after warming up. .

FIG. 3 is a waveform diagram showing changes in cooling water temperature Tw, oil temperature To, and intake valve temperature when the engine is started from the state where the cooling water temperature is 20 ° C. and when the engine is stopped at 80 ° C. after warming up. .

FIG. 4 is a waveform diagram for explaining the operation of the first embodiment.

FIG. 5 is a flowchart for explaining calculation of a wall flow correction temperature Twf.

FIG. 6 is a characteristic diagram of an interpolation coefficient TTC.

FIG. 7 is a flowchart for explaining the calculation of a transient correction amount Kathos.

FIG. 8 is a flowchart for explaining calculation of a fuel injection pulse width Ti.

FIG. 9 is a flowchart that is synchronized with injection timing.

FIG. 10 is a waveform diagram of a conventional example.

FIG. 11 is a diagram corresponding to a claim of the first invention.

[Explanation of symbols]

 2 Control unit 4 Crank angle sensor 6 Air flow meter 11 Water temperature sensor

Claims (5)

[Claims] 1. A means for calculating a basic injection amount according to an operating condition, a means for detecting a cooling water temperature, a means for detecting a physical temperature having a characteristic of rising and falling different from the cooling water temperature, and a physical temperature A means for predicting the intake valve temperature from the cooling water temperature; a means for calculating the equilibrium adhesion amount based on the intake valve predicted temperature, the engine load and the engine speed; and a means for calculating the intake valve temperature, the engine load and the engine speed. And a means for calculating the difference between the calculated equilibrium adhering amount and the adhering amount at that time, and an adhering speed based on the adhering amount of the difference and the calculated adhering amount. And means for updating the adhesion amount by adding the adhesion speed and the adhesion amount in synchronization with fuel injection, and correcting the basic injection amount with the adhesion speed to determine the fuel injection amount. Means for calculation, an air-fuel ratio control apparatus for an engine, characterized in that a means for supplying fuel of the injection amount in the intake pipe. 2. The air-fuel ratio controller for an engine according to claim 1, wherein the physical property temperature is a catalyst temperature, and the intake valve temperature is predicted by interpolation from the catalyst temperature and the cooling water temperature. 3. The air-fuel ratio control device for an engine according to claim 2, wherein the interpolation coefficient is a value corresponding to a difference between the catalyst temperature and the cooling water temperature. 4. The air-fuel ratio control apparatus for an engine according to claim 1, wherein the physical property temperature is an oil temperature, and the intake valve temperature is predicted by extrapolation from the oil temperature and the cooling water temperature. 5. The air-fuel ratio control apparatus for an engine according to claim 4, wherein the extrapolation coefficient is a value corresponding to a difference between the oil temperature and the cooling water temperature.